Subsurface tools, placed downhole within a well, are used for a variety of purposes. Such tools can include packers or plugs, cutters, other similar downhole tools, and setting tools used in conjunction with such devices.
For example, in a typical downhole operation, a packer can be lowered into a well and positioned at a desired depth, and a setting tool can be positioned above the packer in operative association therewith. An explosive power charge is then provided in conjunction with the setting tool. When it is desired to set the packer, the power charge is initiated, which causes gas to be rapidly produced, forcefully driving a movable portion of the setting tool into a position to actuate the packer to seal a desired area of the well. The gas can also provides sufficient force to shear a shear pin or similar frangible member to separate the setting tool from the packer.
The force applied to a subsurface tool by a power charge and/or a setting tool must be carefully controlled. The force must be sufficient to set a packer or to similarly actuate a downhole tool; however, excessive force can damage portions of the downhole tool, rendering it ineffective. Additionally, the power charge must be configured to provide force for a sufficient period of time. An explosive force provided for an extremely short duration can fail to actuate a tool, and in many cases a “slow set” is preferred due to favorable characteristics provided when actuating a tool in such a manner. For example, when setting a packer, a “slow set” provides the packer with improved holding capacity.
Conventional power charges are classified as explosive devices. Most power charges include black powder and/or ammonium perchlorate, and are configured to provide a short, forceful pressure to a subsurface tool to actuate the tool. An explosive force can often create shockwaves within a well bore, which can undesirably move and/or damage various tools and other components disposed within.
Classification of power charges as explosive devices creates numerous difficulties relating to their transport and use. Shipment of explosive devices on commercial carriers, such as passenger and cargo airplanes, is prohibited. Further, shipment of explosive devices via most trucking companies or similar ground transport is also prohibited. Permissible truck, rail, and ship-based modes of transport are burdened by exacting and costly requirements. Shipments of explosives by rail require buffering areas around an explosive device, resulting in inefficient spacing of cargo with increased cost to the shipper. Shipments by truck require use of vehicles specifically equipped and designated to carry explosive devices, which is a costly process due to the hazards involved. Shipment using ships is subject to regulation by port authorities of various nations, grounded in national security concerns, which greatly increases the time and expense required for the shipment.
The difficulties inherent in the shipment of explosive devices are complicated by the fact that numerous oil and gas wells requiring use of power charges are located in remote locales, which are subject to various national and local regulations regarding explosive devices, and which often require numerous modes of transportation and numerous carriers to reach.
Operation of explosive power charges is also restricted, depending on the location in which an operation is to be performed. In many locations, the user of a power charge must be specifically licensed to handle and operate explosive devices. Some nations do not allow transport or use of explosive devices within their borders without obtaining a special permit to requisition a desired explosive device from a designated storage area. In others, various governmental agents or other specialists must be present to ensure safe operation of the device.
In addition to the regulatory difficulties present when using an explosive power charge, the explosive nature of conventional power charges can also inhibit the effectiveness of such devices.
In some instances, a packer or similar subsurface tool can become misaligned within a wellbore. Use of an explosive power charge to provide a short, powerful burst of pressure to actuate the tool can cause the tool to set, or otherwise become actuated, in a misaligned orientation, hindering its effectiveness. While conventional power charges are configured to provide a sustained pressure over a period of time, this period of time is often insufficient to allow a misaligned tool to become realigned within a wellbore, while a longer, slower application of pressure (a “slow set”) can cause a tool to become aligned as it is actuated. Additionally, a longer, slower application of pressure to a subsurface tool can improve the quality of the actuation of the tool, as described previously.
A further complication encountered when using explosive power charges relates to the heat transfer created by the device. Conventional power charges can heat a subsurface tool to temperatures in excess of 2,000 degrees Fahrenheit. These extreme temperatures can cause excessive wear to tool components, leading to the degradation of one or more portions of the tool.
A need exists for a power source, usable as an alternative to conventional power charges, that does not contain explosive substances, thereby avoiding the difficulties inherent in the transport and use of explosive devices.
A further need exists for a power source that provides a continuous pressure to a subsurface tool over an extended period of time, enabling alignment of misaligned tools and improving the quality of the actuation of the subsurface tool, while providing an aggregate pressure equal to or exceeding that provided by conventional power charges.
A need also exists for a power source that provides pressure sufficient to actuate a subsurface tool without increasing the temperature of the tool to an extent that can cause significant damage or degradation.
The present invention meets these needs.